1. Field of the Invention
The present invention relates to a home agent, and in particular to a home agent for designating a transmission period of a binding update packet transmitted from a mobile node.
In recent years, accompanied by mobile nodes increasing, Mobile IP has been predominant as a protocol capable of accommodating both of the mobile nodes and fixed nodes and supporting seamless communication of the mobile nodes over an IP network.
In this Mobile IP, the mobile nodes are required to notify Care-of Addresses (hereinafter, occasionally abbreviated as COA's) indicating moving destination addresses to a home agent.
2. Description of the Related Art
FIG. 21 shows a binding registration process in a general mobile IP network 400, which includes a home agent 110, a subordinate mobile node 300, and access routers 201 and 202. The mobile node 300 can be connected to the network 400 through the home agent 110, and the access routers 201 and 202.
The mobile node 300 has a home address of “HA—1”, and a packet addressed to the mobile node 300 is transmitted to the home address HA_1.
When moving to a link under the access router 201 from a link (home link) under the home agent 110 along a movement {circle around (1)}, the mobile node 300 receives an advertisement message from the access router 201. If a network address of the access router 201 is different from that of the mobile node 300 itself, the mobile node 300 detects itself having moved, acquires a care-of address COA_1 for the access router 201, and notifies the care-of address COA_1 to the home agent 110 with a binding registration message 801_1.
When receiving the packet addressed to the mobile node 300 (destination address HA_1), the home agent 110 transfers this packet to the access router 201 with the care-of address COA_1. Thus, the packet addressed to the mobile node 300 is delivered to the mobile node 300 through the access router 201.
Furthermore, when moving to a link under the access router 202 along a movement {circle around (2)}, the mobile node 300 similarly notifies a care-of address COA_2 for the access router 202 to the home agent 110 with a binding registration message 801_2. The home agent 110 transfers the received packet addressed to the mobile node 300 to the mobile node 300 through the access router 202.
FIG. 22 shows a format of a header of a general Binding Update packet (hereinafter, occasionally abbreviated as BU packet) indicated in the IETF Internet Draft (draft-ietf-mobileip-ipv6-15.txt).
This header is composed of an IP header and a destination option. The IP header includes a source address field 804a and a destination address field 804b. The destination option includes a home address field 804c of a node.
The format of the BU packet is common to those of the binding registration message, a binding change message, and a binding renewal or update (hereinafter, represented by “renewal”) message described later. Hereinafter, the binding registration message, the binding change message, and the binding renewal message may be generally referred to as a binding update packet (hereinafter, occasionally abbreviated as BU packet).
In the source address field 804a, the destination address field 804b, and the home address field 804c of the header of the binding registration message 801_1 shown in FIG. 21, the care-of address COA_1 of the mobile node 300, the address of the home agent 110, and a home agent address of the mobile node 300 are respectively set.
FIG. 23 shows a binding renewal of a mobile node in a general mobile IP network.
The mobile IP network 400 includes the home agent 110, the access routers 201-203, and mobile nodes 301-303 respectively connected to the links of the access routers 201-203.
In the mobile IP network 400, when e.g. the mobile node 301 performs a movement {circle around (1)} as shown in FIG. 21, transmits the binding registration message 801_1 to the home agent 110, and then remains connected to the link of the access router 201 without a movement {circle around (2)}, the mobile node 301 periodically transmits a binding renewal message 802_1 in order to request an extension of a communication time from the home agent 110. In the source address field 804a of the binding renewal message 802_1, the present care-of address COA_1 of the mobile node 301 is set.
The home agent 110 returns a response message 803_1 for the binding renewal message 802_1 to the mobile node 301.
Similarly, while remaining connected to the links of the access routers 202 and 203 respectively, the mobile nodes 302 and 303 periodically transmit binding renewal messages 802_2 and 802_3 to the home agent 110. The home agent 110 returns response messages 803_2 and 803_3 respectively for the binding renewal messages 802_2 and 802_3 to the mobile nodes 302 and 303.
These response messages include a transmission period fixedly set in the binding renewal messages by a manager of the mobile IP network.
Hereafter, each of the mobile nodes transmits the binding renewal messages to the home agent 110 at the received transmission period.
FIG. 24 shows a header format of a general Binding Acknowledgement packet (hereinafter, occasionally abbreviated as BAck packet).
The format of this BAck packet is common to those of response packets from the home agent 110 for the binding registration message, the binding change message, and the binding renewal message transmitted from the mobile node. Hereinafter, the response packets for the binding registration message, the binding change message, and the binding renewal message may be generally referred to as response messages.
The header of the BAck packet is composed of the IP header and a binding acknowledgement sub-option. The IP header includes a source address field 808a and a destination address field 808b in the same way as the header of the binding update packet. The binding acknowledgement sub-option includes a refresh field 808c, in which the above-mentioned fixed transmission period is set.
In such a method by which a prior art home agent transmits a fixed transmission period of a binding renewal message to a mobile node, the mobile node frequently transmits the binding renewal message to the home agent even when the mobile node does not move very often between access routers. This means the increase of the messages within the mobile IP network.
Also, when the scale of the mobile IP network is expanded so that the number of mobile nodes managed by the home agent 110 increases, the binding renewal messages periodically received by the home agent 110 also increase.
Thus, the capacity of the home agent 110 is pressed by reception processing of the binding renewal message, i.e. BU reception processing and BAck transmission processing between the reception of the binding renewal message (BU packet) and the transmission of its response message.
As a result, the following issues arise:    (1) Suspension of other processes under operating conditions, which may secondarily arise by processing load of the binding renewal message reception and the BAck transmission;    (2) Resending of the binding renewal message from the node since the response message for the binding renewal message can not be returned at the time of CPU congestion; and    (3) Further congestion of the mobile IP network by the increase of the number of messages accompanied by (2).